1. Field of the Invention
The invention relates generally to a method of manufacturing semiconductor devices and, more particularly, to a method of forming a micro pattern in a semiconductor device, in which a micro pattern has a pitch lower than the resolution capability of the exposure apparatus.
2. Discussion of Related Art
In manufacturing semiconductor devices, the minimal pitch of a pattern formed in the photolithography process is determined by the waveform of exposure radiation used. Therefore, to form patterns having smaller pitch as semiconductor devices become increasingly integrated, radiation having a waveform shorter than that of the radiation that is currently used must be used. To this end, it may be preferred that X-ray or E-beam be used. However, the use of X-ray or E-beam has not yet been commercialized due to technical problems, productivity, etc. In view of the above, a Dual Exposure and Etch Technology (DEET) has been proposed.
FIGS. 1a to 1c are views illustrating dual exposure etch technology. As shown in FIG. 1a, a first photoresist PR1 is coated on a semiconductor substrate 10 having a to-be-etched layer 1. After the first photoresist PR1 is patterned by exposure and development processes, the to-be-etched layer 11 is etched using the patterned first photoresist PR1 as a mask. The etched to-be-etched layer 11 has a line width of 150 nm and a space width of 50 nm.
Thereafter, the first photoresist PR1 is stripped and a second photoresist PR2 is then coated on the entire structure. The second photoresist PR2 is patterned by exposure and development processes so that some of the to-be-etched layer 11 is exposed as shown in FIG. 1b. 
As shown in FIG. 1c, the to-be-etched layer 11 is again etched using the patterned second photoresist PR2 as a mask, thus forming a final pattern whose line and space width is 50 nm. The second photoresist PR2 is then stripped.
In the above-described dual exposure etch technology, during the exposure process of the second photoresist PR2, the overlay accuracy is directly related to Critical Dimension (CD) variation of the last pattern. In practice, since the overlay accuracy of the exposure apparatus is difficult to control to 10 nm or less, it is difficult to reduce the CD variation of the last pattern. It is also difficult to control Optical Proximity Correction (OPC) through the separation of circuits depending on exposure.